1. Field of the Invention
Illustrative embodiments of the present disclosure relate to an ink cartridge and an image forming apparatus employing the ink cartridge, and more specifically to an image forming apparatus including a recording head for ejecting droplets of liquid and an ink cartridge removably mounted in the image forming apparatus.
2. Description of the Background
Image forming apparatuses are used as printers, facsimile machines, copiers, multi-functional peripherals having two or more of the foregoing capabilities, or plotters. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head for ejecting droplets of ink.
In image formation, such image forming apparatuses employing the liquid-ejection recording method eject droplets of ink or other liquid from the recording head onto a recording medium to form a desired image (hereinafter “image formation” is used as a synonym for “image recording” and “image printing”). Such liquid-ejection-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving the recording head in a main scan direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus.
With recent increases in the operation speed, such liquid-ejection-type image forming apparatuses (hereinafter also referred to as “inkjet recording apparatus”) have become widespread for not only home use but also business use. Further, there is an increased demand for forming an image on a recording medium of a large width. For business use, such an inkjet recording apparatus is provided with an ink cartridge capable of storing a large volume of ink, to reduce the frequency of cartridge replacement.
Accordingly, instead of a system in which the ink cartridge is directly mounted on the recording head, such inkjet recording apparatuses may employ a system in which the ink cartridge (also referred to as “main tank” or “main cartridge”) is removably mounted in the image forming apparatus and connected to the recording head mounted on, e.g., a carriage via a tube to supply ink, an arrangement that is also referred to as a tube supply system.
With the tube supply system, ink consumed for image formation is supplied from the ink cartridge to the recording head via the tube. However, this system is not without its problems. For example, using a flexible thin tube may cause substantial fluid resistance for ink passing through the tube and prevent ink from being supplied on time for ink ejection, resulting in ejection failure. In particular, a large-size image forming apparatus that forms an image on a large-width recording medium necessarily uses a relatively long tube, resulting in increased fluid resistance of the tube. Further, high-speed recording or ejection of high-viscosity ink may increase the fluid resistance of the tube, causing ink supply shortage in the recording head.
Hence, for example, in one conventional technique like that described in JP-3606282-B, ink is kept at a pressurized state in the ink cartridge and a differential-pressure regulating valve is disposed upstream of the recording head in the ink supply direction to supply ink when negative pressure in the sub tank exceeds a threshold level.
Such a configuration may prevent the above-described ink supply (refill) shortage. However, as ink is pressurized, positive pressure may remain in the ink supply pathway. Consequently, when the ink cartridge is removed from the recording apparatus, such residual pressure may cause ink leakage from a connecting portion between the ink cartridge and the inkjet recording apparatus.
Hence, in another conventional technique like that described in JP-3775650-B, a valve that regulates air pressure to pressurize ink is driven with an electromagnetic plunger to release the pressure in the air passage to prevent such ink leakage. Similarly, in still another conventional technique like that described in JP-2008-230010-A, ink is supplied with air pressure from the ink cartridge via the ink supply pathway. A portion of the ink supply pathway is made of a flexible film so as to be able to change volume, and the ink cartridge is pressurized with air from the outside. With such a configuration, when the ink cartridge is removed, the ink supply pathway itself absorbs the residual pressure of ink to prevent ink leakage.
However, the configurations of the above-described conventional techniques like those of JP-3775650-B and JP-2008-230010-A are intended simply to release the air pressure and thus may not prevent ink from leaking from the ink cartridge or the connection portion of the inkjet recording apparatus when the ink cartridge is removed from the inkjet recording apparatus.